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Guest Ron Freimuth

Engine modelling is incorrect. How would one change it?

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Caveat: programming my VCR and doing some stuff with macros is about the limit of my experience.The aspect that is wrong is that when the prop lever is pulled back on one of the constant speed planes, the fuel flow shoots up. This shouldn't happen, as the pistons are turning slower and less fuel/air is coming through the induction system. Over on a simflight.com FAQ it says that this is in fact correct performance, but this contradicts real life and logical evidence.Where is the data that governs engine performance found? Is it feasible to manipulate it?Thanks in advance.

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I am not an expert but as far as I know fuel flow primarily depends on manifold setting (power) alone. It is true that with lower rpm props are turning slower but they also have a lot more resistance to overcome due to higher blade angle. So in the "first-order" of approximation fuel flow should in fact remain constant.Michael J.

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<<<>>>Not according to this in-flight data from a real engine logging parameters as it was flown.http://www.avweb.com/articles/pelperch/pelp0008.html(Scroll down and have a look at the charts. They are annotated, and it clearly shows that when this pilot pulled the prop control back without touching the throttle, the fuel flow dropped.)Also, manifold pressure is simply a combination of how open the throttle plate is and how much the pistons are sucking air.<<<>>The prop control sets a desired RPM, not a desired blade angle. The blade angle will initially increase, loading the engine and slowing it down. Then, the governor will change the angle to maintain the desired setting. <<<>>Once again, it isn't this way in real-flight data. And in FS2002 it actually goes UP.I am certainly no expert either, but I'm very close to sure that the way it is in FS2002 is wrong.

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<<< It is primarily about mixture leaning techniques. Nothing in this article contradicts what I said - fuel flow is proportional to the work performed by the prop.>>>Yup, it is primarily about mixture leaning (fascinating series of articles aren't they, by the way?), but at this point in logging the data the mixture control hasn't been touched. All that has been touched is the prop control: from 2700 RPM to 2500 RPM. The fuel flow clearly goes down, yet in FS2002 it goes up by a pretty huge amount. That's the behaviour that's puzzling me.

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Vmca...That's a good article. I've bookmarked it for a later reading.I haven't noticed your issue as much as I have that when we change the mixture on the engines,we don't see any change in fuel flow, CHT or EGT.So, when I'm decending from or climbing to an alitude, I just pretend that I'm changing fuel flow...I go through the motions.If it bothered me bad enough, I guess I'd learn how to design gauges.http://www.cableone.net/joesumralliii/hook.gif

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The article touches upon the favorite discussion topic - how to lean - on the rich or lean side of the curve. The last issue of FLYING has a big article on the subject. Needless to say it is a highly debated, controversial subject, even Lycoming and Continental engineers are not in full agreement.Michael J.

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<<<>>>And how. Even more so than religion and politics.

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>I am not an expert but as far as I know fuel flow primarily >depends on manifold setting (power) alone. It is true that >with lower rpm props are turning slower but they also have a >lot more resistance to overcome due to higher blade angle. >So in the "first-order" of approximation fuel flow should in >fact remain constant. >>Michael J.I take it back .. Michael J.

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>The aspect that is wrong is that when the prop lever is >pulled back on one of the constant speed planes, the fuel >flow shoots up. This shouldn't happen, as the pistons are >turning slower and less fuel/air is coming through the >induction system. Over on a simflight.com FAQ it says that >this is in fact correct performance, but this contradicts >real life and logical evidence. >>Where is the data that governs engine performance found? Is >it feasible to manipulate it? MSFS people must not know much about engines. TBL 508 is wrong in many of their AIR files. Torque increases a lot around 2100 RPM. This is incorrect.Ron

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<<<>>>As chance would have it, I d/l'd the superb 421C Golden Eagle and, lo and behold the engines behave as they should.Obviously, it ~is~ possible for it to be modelled correctly in FS2002. It just isn't in the default planes.

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So you like Flight1's Cessna 421C ?Tell me about its flight director (not sure it has one). But in case it has one is it working correctly ? For some reason this piece of instrument is giving many developers trouble yet FS2002's default airplanes have it working just fine.Michael J.

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Hi. You are right. All, or most, MSFS engine/flight dynamic models are not correct. If you want something that you can use, you have to look/beg for the Ron and Steve

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<<>>It doesn't.One other thing it doesn't seem to have is an ADF or an RMI (unless I'm mistaken). I'd really like to add one because we still have plenty of them here in Australia.However, IMHO, it's a great plane.

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